The present invention relates generally to pain reduction systems and more particularly to pain reduction utilizing electromagnetic electrodes proximate the cerebral cortex, vagus nerve and thoracic dorsal root nerves.
Seldom are any surgical or therapeutic procedures performed without the perception of pain on the part of the patient. The medical specialty of anesthesiology has been developed to a high degree of sophistication for the relief and control of pain during surgery. Most application for pain relief use various chemical moieties delivered over numerous routes and modalities.
There are less conventional means of pain relief known comprising such entities as transcutaneous electrical nerve stimulators (TENS). These TENS units have received application retrospectively for local pain relief following surgical procedures.
The perception of pain is the end result of a process that began with stimulation of a peripheral sensory nerve and culminating in the conscious awareness of the pain at the cerebral cortex. Within the central nervous system there are several levels of organization at which the perception of pain may be interrupted. Perception begins with stimulation of a distal peripheral sensory nerve. The stimulation signal travels to the next level of sensory collection which is at the dorsal sensory nerve root ganglion just lateral to the spinal cord. The path then enters the spinal cord to the sensory tracts and ascends the spinal cord to the brain stem. Form the brain stem the sensory tracts then traverse to and innervate the thalami in the midbrain area. From the thalami the sensory stimulations are projected onto the cerebral cortex along the sensory strip. Each area of the cortex in this strip represents a surface area of the body in a fashion known as the homunculus distribution of the cerebral cortex.
Various procedures have been employed in the past to interrupt the perception of pain at these various levels, Peripheral nerve blockade is achieved through various methods, the more notable and commonplace are local nerve blocks with use of chemicals such as lidocaine injected at the procedure site. Dorsal root sensory ganglion blockade is achieved through spinal anesthesia by placing a chemical anesthetic agent such as lidocaine or one of its congeners within the spinal canal. Suitable narcotics, such a morphine, are also available for use within the spinal canal. The higher levels of sensory perception are interrupted through the modality known as general anesthesia. Such a method renders the patient unconscious during the period of general anesthesia.
It is in the area of local peripheral sensory nerve blockade that TENS units exercise their effect. Such units are applied in the area of the surgical wound after the procedure and set to deliver an electrical stimulus locally to the peripheral nerve endings. Similar TENS units have been utilized somewhat more proximal along the length of the peripheral nerve by applying the TENS unit to the ski of the back over the mid line area in an attempt to provide electrical stimulation to the dorsal spinal nerves as they exit the spinal column.
Chemical anesthetics used in local, regional and general anesthesia have numerous characteristics. A number of chemicals are available for local tissue injection providing direct anesthetic block at the sensory nerve ends. Other chemicals are for intravenous delivery and disseminate throughout the entire body to produce a general anesthesia effect. Intermediate to this, chemicals have been developed for direct injection into nerve bundles providing a regional type of anesthetic block, Such examples of regional anesthesia are axillary nerve blocks putting the arm to sleep, sacral nerve blocks putting the back of the leg to sleep, saddle blocks or epidural blocks that render the entire lower half of the body anesthetized.
Besides liquid injectable anesthetic agents, numerous gases are available for inhalation use in general anesthesia. Few of the gases are designed specifically for only pain relief. Instead, virtually all of these gases have been designed to render the patient unconscious as the main method of providing pain control. A notable exception is nitrous oxide when used during dental procedures. Nitrous oxide acts as an anxiolytic, altering the patient""s apprehension of pain but not completely removing or ablating the perception of pain.
The liquid and gas chemicals all share numerous complications. All of these agents must be introduced within the patient""s body where they undergo their primary purpose but must then be eliminated by the body. Each patient is different in their physiologic reaction to a chemical in terms of depth of anesthetic effect, elimination, duration of anesthetic effect, and sensitivity to toxic or allergic reactions. A number of these chemical agents are altered metabolically to undergo elimination. These metabolic intermediates may or may not have primary anesthetic activity and they may add to the toxic complications. Unlike electricity, which effect can be turned on and off virtually instantaneously, chemicals remain within the body until the body is able to eliminate them.
The number of complications secondary to all of these anesthetic chemicals are numerous. However, the general categories of these complications are toxicity in its various forms, allergic reactions, and hyper- or hypo-response to the primary effect of the anesthetic agent. Some of the more profound reactions can lead to death, especially in the area of general anesthetic delivery which has a death rate of approximately 1 per 50,000 to 100,000 general anesthetic procedures.
The primary purpose of anesthesia is the control of pain, with desired secondary effects to control patient apprehension and anxiety. Obviously the more complex and involved cases, such as open heart surgery, lung surgery, and intra-abdominal surgery carry tremendous psychological overtones along with the perception of pain. General anesthesia for pain relief and control of patient apprehension is appropriate.
Numerous other less intense surgical procedures are amenable to regional and local anesthetic control allowing the patient to remain conscious during the procedure. Numerous examples range from cranial burr holes for stimulation of the cerebral cortex in mapping procedures to facial surgery, arm and hand surgery, breast biopsies, abdominal hernia surgery, prostate and urinary bladder surgery, leg and foot surgery. In all of the above procedures, prospective pain control is in the form of gas or liquid chemical agents introduced into the patient""s body.
A number of procedures are carried out in urgent to emergent circumstances where there in no time to provide adequate prospective pain control. A specific example is the administration of automatic cardioversion/defibrillation shock therapy via an implanted device. These units are designed to respond to cardiac fibrillation or tachycardia and convert the dysrhythmia before the patient suffers any ill effects from the dysrhythmia. The electrical shock therapy delivered to the heart is of high voltage and moderate current causing considerable pain to the patient when it is delivered. No means exist to prospectively block this pain. The perception of pain in patients undergoing cardioversion/defibrillation is mediated through the vagi nerves innervating the heart and peripheral nerves within the chest wall. The pain signals traverse the vagi nerves directly to the brain stem and into the thalamic region of the midbrain. Pain stimulation through the thoracic chest wall peripheral nerves traverses these nerves back to the dorsal root sensory ganglia and into the spinal cord at each vertebral level where the signal is carried up the spinal cord. From this point the perceived pain stimulus disseminates to the appropriate area of the cerebral cortex corresponding to the area of the body from which the signal was received. In this fashion perception of pain is then brought to the conscious awareness of the patient and associated with that specific area of the body.
Perception of pain via the vagus nerve is of a more diffuse generalized sensation due to the nature of the nervous system in perceiving pain from the major thoracic and abdominal organs. Pain perceived via the vagus nerve is described as a pressure pain sensation within the chest and is diffuse, to the extent that the patient is not certain that it comes from the heart specifically but rather the chest generally, In contrast, perception of pain from stimulation of the chest wall peripheral nerves is specific to the area stimulated, and the patient knows exactly where the pain originates.
Prospective pain relief in the circumstances of anticipated cardioversion/defibrillation counter shock therapy in only available at this time in elective cardioversion/defibrillation procedures. The general practice is to provide an anxiolytic agent, such as those known under the trade names Valium(copyright), Versed(copyright), or Ativan(copyright), and an ultra-short acting general anesthetic agent, for example that known under the trade name Brevitol(copyright), from the barbiturate family.
Numerous surgical and therapeutic procedures result in the patient experiencing pain in the area of the body undergoing the procedure. The invention discloses systems and methods for providing pain relief in anticipation of any surgical or therapeutic procedure, including cardioversion/defibrillation. Pain relief is preferably accomplished by electromagnetic stimulation of appropriate nerve structures.
This invention disclosed means for positioning appropriate electrodes proximate the nerve structures that innervate the area of receive stimulation from the area where the procedure is carried out. Stimulation of the appropriate nerves achieves a blocking of the transmission of the sensory signal and is perceived as anesthesia.
The invention further discloses means for providing further pain relief by direct cerebral cortical stimulation of the sensory area of the cortex that corresponds to the area of the patient""s body undergoing the painful procedure.
The above and other objects and advantages will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.